1. Field of the Invention
The present invention relates to catheters which are inserted into blood vessels and used to inject radiopaque dyes or to otherwise aid in medical treatment of a human or mammal.
2. Description of the Prior Art
The prior art contains a number of catheters designed for intravascular use in the treatment of disease including the injection of radiopaque dye into a blood vessel. Generally these catheters include a relatively stiff and strong body portion having a soft tip portion on the leading end. The stiff body portion is required to provide torqueability, burst pressure strength, and longitudinal rigidity or column strength for advancing the catheter in the vessel. Torqueability is required to enable the catheter to be twisted so a curved tip may be directed into a desired vessel. Burst strength is required to permit injection of fluids under pressure without ballooning or bursting of the catheter wall. Longitudinal rigidity or column strength is necessary to permit advancement of the catheter in a vessel by pushing on an exterior end of the catheter. The soft tip is necessary to avoid trauma and injury to the blood vessel walls which can be caused if the relatively stiff polymeric material is used in the tip portion.
Angiography catheters having a stiff body portion have been formed in the past by forming the polymer body portion with a braid to produce the desired stiffness, and either leaving the braid out during the forming of the tip portion or fusing a soft tip of the same or a similar polymer to the braided body portion. Additionally, angiography catheters have been constructed by coextruding inner and outer tubular polymer materials in the body portion with a soft polymer material extending beyond the stiff polymer tubular portion to form a soft tip portion. In catheters having soft tips which are fused, the polymer of the body portion and the polymer of tip portion must be substantially the same chemically since it has heretofore been impossible to fuse a soft polymer to a rigid polymer which is chemically substantially different.
Prior art catheters have been made from a variety of polymeric materials including polyurethane, polyethylene, nylon and PVC. Nylon, such as nylon-11, is a polymer that provides excellent stiffness characteristics when extruded into tubes of diameters in the range from 2 Fr. to 10 Fr. to produce catheters having excellent torqueability, burst strength characteristics, and longitudinal rigidity. The stiffness of the nylon tubes, however, results in a tip which is too stiff and which may cause vessel injury. Soft nylon materials generally contain plasticizers which may leach out while the catheter is in the vessel and thus are not suitable for forming soft tips.